i have a 2004 chevy 2500 duramax/allison 5spd auto extended cab 2x4 8' bed. i have a f250 work top on the truck so it is not very areodynamic right now. in town i get about 12-15 i pull alot of trailers so sometimes i get lower on the hwy i get more but hard to tell mostly drive around town. i think i got 18+ going to savannah when it was new without the top i got 19 on the hwy. i had a 2002 f250 with the 7.3 powerstroke and got the same mpg's hope this helps.... after having 4 diesel trucks and 2 gas trucks i will never go back to gas....